Method for formation of polymer

ABSTRACT

Objects of the present invention are to provide a method for molding polymers to be able to mold products each of which has an outer shape transferred accurately from the shape of the inside of a mold, exhibits high dimensional accuracy and is uniform in the thickness of its surface skin layer and the expansion ratio in its foamed inside. 
     A molten polymer  60  is injected into a cavity  30  and simultaneously gas is pressed to the inside of the molten polymer  60  to contact the polymer close to the surface of the mold, and then gas is exhausted while maintaining the shape inside the mold, to thereby mold a polymer formed product in which a surface skin layer  61  and a foamed inside  62  having cushioning property are formed in one piece.

FIELD OF THE INVENTION

The present invention relates to methods for molding polymers, and moreparticularly to methods for molding a product in which a skin layer anda cushiony inside are formed in one piece by using the same polymers,whereas the term “polymers” refers to “thermoplastic resins,”“thermoplastic elastomers,” “thermosetting resins” or “cross-linkedelastomers.”

RELATED ART

Molded products, each having a skin layer and a cushiony inside, areused for various purposes, such as automotive interior panels to meetthe requirements of posh appearance and softness of touch.

The molded products, each of which a skin layer and a cushiony insideare formed in one piece, can be molded by covering a cushiony material,such as polyurethane foam, with vinyl chloride or the like.

Recently, in response to requirements of high recycling efficiency andefficient cost reduction by simplifying processes, molded products, eachhaving a skin layer and a cushiony inside and molded using the samematerial in one piece, have been provided.

There have been disclosed techniques for molding a product having a skinlayer and a cushiony inside formed in one piece by using the samematerial in, for example, the Japanese Patent Publications Laid-OpenNos. 7-80885 and 7-88878.

The Japanese Patent Publication Laid-Open No. 7-80885 describes atechnique for obtaining a molded product with a desired expansion ratioand an adequate mold surface transferability in reference to aninjection molding method for obtaining a molded product having a skinlayer containing a foam part by injecting a resin containing a foamingagent into a cavity within a mold clamped in an openable way andoperating the mold to have said mold cavity enlarged and the resinfoamed, so that the skin layer is cooled and solidified when it contactswith the inside surface of the mold. The desired expansion ratio and theadequate mold surface transferability of the 7-80885 are obtained byenlarging the mold cavity at a suitable speed and selecting a suitableresin, etc.

The Japanese Patent Publication Laid-Open No. 7-88878 describes atechnique for obtaining a molded product with desired feel bycontrolling the operating speed for enlarging a mold cavity according tothe pressure within a mold in reference to an injection molding methodsimilar to the injection molding method described in the Japanese PatentPublication Laid-Open No. 7-80885.

DISCLOSURE OF THE INVENTION

According to the techniques described in the Japanese PatentPublications Laid-Open Nos.7-80885 and 7-88878, a molten resincontaining a foaming agent is injected into a cavity within a mold andthen the mold is operated in such a way that the mold cavity full ofsaid molten resin is enlarged and thereby the resin is foamed. Forexample, as illustrated in the upper and lower schematics of FIG. 5,when a lower mold 120 is displaced leftward as viewed in this figure,the mold cavity full of a molten resin 160 is enlarged and pressurewithin the mold is lowered, and an molded product having a skin layer161 and an internal foaming part 162 formed in one piece is obtained.

However, the techniques described in the Japanese Patent PublicationsLaid-Open Nos. 7-80885 and 7-88878 have problems as described below:

Firstly, as the molding space (i.e., mold cavity) is enlarged anddeformed in the process of molding, it may be difficult to preciselytransfer the inside shape of a mold cavity to the outside shape of amolded product, and thus dimensional precision may be lowered.Furthermore, in order to precisely transfer the inside shape of a moldcavity to the outside shape of a molded product, it is necessary toprecisely control the enlargement of the molding space, and this willincrease the cost.

Secondly, as the enlargement of the molding space is different from oneportion to another, the thickness of the skin layer 161 and theexpansion ratio of the foam part 162 vary from one position to another.As a result, the appearance, feel and the like of a molded product varyfrom one position to another. For example, for a molded product withcross-sectional shape as illustrated in FIG. 5, while the thickness ofthe vertical portion as viewed in this figure is changed from T0 to T1when the molding space is enlarged, the thickness of the upper and lowerhorizontal portions remains unchanged at t0. This inevitably causesscattering to the appearance and feel of the molded product between thevertical portion and the upper and lower horizontal portions.

Thirdly, due to the shape of products to be molded, there are somerestrictions on structuring molds about the direction in which themolding space is to be enlarged. For this reason, however well the moldstructure is contrived, the second problem described above may not besolved completely.

The primary object of the present invention is to solve these threeproblems described above.

It has been demanded that a molded product having a skin layer and acushiony inside both molded with the same material should be providedwith desired posh appearance by improving the transferability to such anextent that the mirror finished surface and/or embossed surface can becompletely transferred.

The secondary object of the present invention is to satisfy this demand.

The primary object of the present invention can be achieved byconstructions as described below in which pressure on a molten resinwithin a mold cavity without deforming the mold cavity and thereby theinside of the molten resin within the mold cavity is foamed.

The present invention relates to a method for molding polymers in whicha molten polymer containing a foaming agent is put into a mold cavityand contacted in the molten state close to the mold cavity surface, andthen the volume occupied by said polymer is increased while the insideshape of the mold cavity is maintained to obtain a molded product havingthe outside shape thereof fit to the inside shape of the mold cavity andthe inside thereof foamed.

According to the present invention, as the mold cavity remainsunchanged, the dimensional precision of a molded product is high.Furthermore, the thickness of a skin layer and the expansion ratio of afoam part are uniform, and there is no differences in appearance andfeel from one portion to another.

A method for putting a polymer containing a foaming agent into a moldcavity may be realized in a method in which a polymer in the moltenstate is put into a mold cavity as seen in injection molding methods,and also a method in which a polymer is put into a mold cavity and thenheated and molten as seen in compression molding methods.

Said volume occupied by a polymer refers to a volume occupied by apolymer injected by one shot into a mold cavity by an injection moldingmethod or a volume occupied by a polymer put in a mold cavity by acompression molding method.

As a specific example of methods for increasing said volume occupied bya polymer while the inside shape of a mold cavity is maintained, inaddition to methods described below, there is a method in which a pinpositioned within a molten polymer is pulled out with specified timing.

Here, it should be noted that the skin layer of a molded product withthe outside shape thereof fit to the inside shape of a mold cavity andwith the inside made foamed is formed as a non-foamed skin.

The present invention relates to a method for molding polymers in whicha polymer containing a foaming agent is put into a mold cavity, gas isinjected into said polymer to contact the polymer in the molten stateclose to the mold cavity surface by utilizing the pressure of said gas,and said gas is exhausted to fill the space occupied until then by saidgas with the polymer and thereby increase the volume occupied by saidpolymer and foam said polymer to obtain a molded product having theoutside shape thereof fit to the inside shape of the mold cavity and theinside thereof foamed.

According to the present invention, as the volume occupied by the moltenpolymer is increased by the exhausting gas, the pressure when the gas isexhausted can be easily adjusted as well as the dimensional precision ofmolded products is high and there is no differences in appearance andfeel from one portion to another. Therefore, an effect that thethickness of a skin layer and the expansion ratio of a foam part can beeasily adjusted to desired thickness and expansion ratio respectivelycan be obtained.

The present invention can be embodied as a molding method in, forexample, a gas-assisted injection molding method by exhausting the gasafter the skin layer contacted close to a mold cavity surface is cooledand solidified and filling the space occupied until then by said gaswith the polymer and then foaming said polymer. Here, the gas-assistedinjection molding method refers to an injection molding method in whichhigh-pressure gas is injected into a molten resin at the same time whensaid molten resin is injected into a mold. This method can improve theadherability of the molten resin to a mold face and also improve thefluidity of said molten resin to quickly go around all over the moldface. When the gas-assisted injection molding method is applied, ahollow and light-weighted molded product with no flection and with hightransferability can be obtained.

When exhausting the gas, it is preferable that such exhausting should becontrolled so that the pressure within the mold cavity can be maintainedto such a level that the skin layer cannot come off from the mold faceand the inside of the molded product can be foamed at a desiredexpansion ratio.

According to the present invention, a molded product having desiredappearance and desired cushion performance can be obtained by performingcomparatively easy control, i.e., adjusting the pressure of the exhaustgas so that the pressure within the mold cavity can be lowered on adesired pattern. Here, the desired pattern refers to, for example, apattern in which the pressure within the mold cavity is comparativelyquickly lowered in the early stage when the foaming power is strong andthe pressure is slowly lowered in the last stage when the foaming poweris weak.

The present invention relates to a method for molding polymers in whicha polymer containing a foaming agent is put into a mold cavity, thensaid polymer is contacted in the molten state close to a mold cavitysurface, and then a part of said polymer is released in the molten stateinto a shelter communicated with said mold cavity, and thereby thevolume occupied by said polymer in the molten state is increased toobtain a molded product having the outside shape fit to the inside shapeof the mold cavity and the inside thereof made foamed.

According to the present invention, as the volume occupied by the moltenpolymer can be increased by releasing a part of the polymer into theshelter, the extent of lowering the pressure can be set by setting thesize of the shelter accordingly, as well as the dimensional precision ofmolded products is high and there is no differences in appearance andfeel from one portion to another. Therefore, an effect that theexpansion ratio of a foam part can be easily adjusted to a desired scalecan be obtained.

The present invention can be embodied as a molding method in which, forexample, a shelter and a mold cavity are communicated with each other,the communication of said shelter and mold cavity is maintained shut offby a shutter until a polymer containing a foaming agent is contacted inthe molten state close to a mold cavity surface and a skin layer iscooled and solidified, and said shutter is opened to make both theshelter and the mold cavity communicated with each other with timing inwhich the skin layer is formed.

The present invention may also be embodied as a molding method in whicha shelter and a mold cavity are always maintained in communication witheach other by means of a comparatively thin passage, and a process inwhich a polymer containing a foaming agent is contacted in the moltenstate close to a mold cavity surface and a skin layer is cooled andsolidified and a process in which a part of the molten polymer isreleased into the shelter and thereby the volume occupied by saidpolymer is increased are carried out at the same time in parallel. Whensaid molding method is practiced in an injection molding method, it ispreferable that the speed of the injected polymer spreading all over themold surface should be properly adjusted to make the skin layer quicklyformed. This adjustment of the speed maybe performed, for example, byadjusting the temperature of the mold surface etc.

The secondary object of the present invention can be achieved byconstructions as described below in which the pressure on a molten resinwithin a mold cavity is lowered without deforming the mold cavity andthereby the inside of the molten resin within said mold cavity isfoamed, and furthermore the temperature of the mold surface ismaintained to a certain temperature level or higher until the moltenpolymer is completely contacted closeto the mold cavity surface.

The present invention is related to a method for molding polymers inwhich the entirety or a part of said mold surface is heat insulated inany of the inventions described above.

According to the present invention, as the mold surface is heatinsulated, an effect that the molten polymer can be completely contactedclose to the mold cavity surface and thereby the mirror finished surfaceand/or embossed surface can be completely transferred, as well as aneffect that the dimensional precision is high and there is nodifferences in appearance and feel from one portion to another, can beachieved.

The heat insulation of the mold surface can be achieved by providing aheat-insulating layer on the skin layer of the mold surface or in theneighborhood of the mold surface that is not so deep from the skin layerof the mold surface. When a heat-insulating layer is provided on theskin layer of the mold surface or in the neighborhood of the moldsurface that is not so deep from the skin layer of the mold surface, asthe mold surface can be heated by utilizing the heat of the moltenpolymer, said polymer can be completely contacted close to the moldcavity surface. Therefore, the mirror surface and/or embossed surfacecan be completely transferred. When an injection molding method is used,since the development of a skin layer can be controlled for acomparatively longer time, the fluidity of the molten polymer can bemaintained for a comparatively longer time, even a thin molded productcan be obtained in good condition. Here, the skin layer refers to a skinlayer solidified when it contacts the mold surface.

Said heat-insulating layer may be provided all over the mold surface andalso may be provided only on a part of the mold surface which shouldhave a high transferability.

For example, in a double injection in which an already molded product isset within a mold cavity and additional injection is made, theheat-insulating layer may be provided only on the mold surface that isnot covered with said product. In this arrangement, an injected goodmolded product with no flection between the already molded product andthe newly injected polymer can be obtained.

When said heat-insulating layer is provided all over the mold surface, aworking effect that the molten state of said polymer can be maintaineduntil the polymer is completely contacted close to the mold cavitysurface and thereby the transferability can be improved can beadequately achieved.

When said heat-insulating layer is provided on the skin layer of themold surface, the surface of said heat-insulating layer serves as atransfer surface. That is, the surface of said heat-insulating layer istransferred in such a way that the outside shape of the molded polymerproduct can be formed.

When said heat-insulating layer is formed in the neighborhood of themold surface, the original mold surface serves as a transfer surface.Here, the neighborhood of the mold surface refers to the rear of themold surface, i.e., the inside of the mold, and a depth allowing thecomplete heating of the mold surface with the heat from the moltenpolymer.

The thermal conductivity of said heat-insulating layer should preferablybe within a range of 0.001 to 0.01 [cal/cm·s·° C.]. If this thermalconductivity is below 0.001 [cal/cm·s·° C.], cooling will require animpractically very long time. On the other hand, if said thermalconductivity is over 0.01 [cal/cm·s·° C.], the transfer surface will becooled down before the molten polymer is completely contacted close tothe transfer sursurface, so that the mold surface will not be completelytransferred.

As examples of a heat insulating material whose heat conductivity iswithin a range of 0.001 to 0.01 [cal/cm·s·° C.], specific silane coatingmaterials, epoxy resins, phenolic resins, fluorocarbon resins andceramics can be named.

The specific silane coating materials includes the hydrolysate oforganosilane expressed by a chemical formula ofR¹Si(OR²)₃  [Chemical Formula 1]and/or a coating material mainly composed of a partially condensedproduct thereof. Here, R¹ indicates the organic group with the carbonnumbers 1 to 8, and R² indicates alkyl group with the carbon numbers 1to 5 or acyl group with the carbon numbers 1 to 4.

The thickness of said heat insulating layer is 0.02 to 3 [mm] andpreferably should be 0.1 to 2 [mm]. If this thickness is below 0.02[mm], as the heat insulating layer will not have an adequate heatinsulating effect, the temperature of the mold surface will not beadequately raised, and the mold surface will not be completelytransferred. If said thickness is over 3 [mm], the heat insulatingeffect will be excessively large, the polymer cooling speed will beexcessively low, cooling to the temperature at which the molded productcan be taken out will require a long time, and therefore, this muchthickness will not be applicable to industrial production.

The heat insurance of the mold surface can also be achieved by providingspaces at the back of the mold surface and increasing the adiathermancyand/or by composing the mold surface with a porous metal and loweringthe heat conductivity.

Making the mold surface porous can be achieved by allocating a porousmetal plate, apart from the main body of a mold, into the mold or makingthe mold surface porous. A porous metal plate can be manufactured bymaking holes within a range of 1 to 200 μm across each, preferablyapprox. 10 μm across each, by using laser, at a density within a rangeof 30,000 to 3,000,000 pcs/cm², preferably within a range of approx.100,000 to 1,000,000 pcs/cm². If the hole diameter is larger than 200μm, a molten resin will enter the holes not only to lower the moldreleasability but also to degrade the surface condition of moldedproducts, which is not preferable. If the hole diameter is smaller than1 μm or the hole density is lower than 30,000 pcs/cm², a desired heatinsulating effect will not be obtained, which is not preferable, either.If the hole density is larger than 3,000,000 pcs/cm², the molddurability will be degraded, which is not preferable, either.

In a structure in which a heat insulating layer is provided over theskin layer of the mold surface or in the neighborhood thereof, spacesare provided at the back of the mold surface, or the mold surface ismade porous to heat insulate the mold surface, a means for secondarilyheating the mold surface may be added. That is, if the heat from themolten polymer alone is not adequate enough to raise the temperature ofthe mold surface, the shortfall from the target temperature may be madeup for by preheating the mold surface by using a secondary heatingmeans.

The present invention relates to a method for molding polymers in whichthe entirety or part of the mold surface is preheated in either of theinventions described above.

According to the present invention, as the mold surface is preheated, aneffect that the molten polymer can be completely contacted close to themold cavity surface and thereby the mirror finished surface and/orembossed surface can be completely transferred, as well as an effectthat the dimensional precision is high and there is no differences inappearance and feel from one portion to another, can be achieved.

The preheating of the mold surface can be achieved by, for example,raising the temperature of the mold surface by injecting heated air orheated nitrogen gas (hereinafter referred to as “temperature controllinggas”) into the mold cavity forming a closed space, and then quicklyexhausting said temperature controlling gas. Here, when the moldingmethods according to the present invention is performed in an injectionmolding method, the molten polymer is supposed to be injected into themold cavity before or almost simultaneously in parallel with the exhaustof the heated air.

The structure exemplified above needs a mechanism for injecting thetemperature controlling gas into the mold cavity, a mechanism forquickly exhausting the temperature controlling gas from the mold cavity,and a mechanism for holding the temperature of the mold surface raisedby the temperature controlling gas for a time required.

As a mechanism for injecting the temperature controlling gas, amechanism, for example, similar to a mechanism used for injecting gas inthe gas-assisted injection molding method may be used. However, as thetemperature controlling gas is used only for raising the temperature ofthe mold surface by flowing within the mold cavity, the pressurerequired for injecting the temperature controlling gas is lower than thepressure required in the gas-assisted injection molding method. Ifappropriate, this mechanism may also be used as a gas injectionmechanism for the gas-assisted injection molding method. A pipingmechanism for injecting the temperature controlling gas may be providedon the injection molding machine side in the same way as the mechanismfor injecting gas into the mold cavity in the gas-assisted injectionmolding method, separately on the mold side, or on both the injectionmolding machine side and the mold side.

The mechanism for exhausting the temperature controlling gas cancomprise, for example, vents opened to the mold surface and a smallnumber of pipes for collectively exhausting the temperature controllinggas passed through said vents. The diameter of said vents should bewithin a range of 10 to 300 μm each, should preferably be within a rangeof 10 to 100 μm each, and more preferably be within a range of 30 to 50μm each. If this diameter is smaller than 10 μm, the gas volatized fromthe molten or softened polymer will condense within the vents and morelikely to clog the vents, which is not preferable. If the diameter islarger than 300 μm, the molten or softened polymer will enter the vents,the polymer molded product will have irregular surface, which is notpreferable, either. The density of said vents should preferably bewithin a range of 1 to 100 pcs/cm², and more preferably be within arange of 1 to 80 pcs/cm², and still more preferably be within a range of1 to 50 pcs/cm². If this density is lower than 1 pc/cm², the temperaturecontrolling gas will not be smoothly exhausted, which is not preferable.If the density is higher than 100 pcs/cm², the heated air will beexhausted excessively faster, and consequently the mold surface will notbe easily set to a desired temperature, which is not preferable, either.

A mechanism for holding the raised temperature of the mold surface cancomprise, for example, a skin layer board having said vents and spacesprovided at the back of said skin layer board. That is, said mechanismcan be realized by heat insulating the skin layer. The spaces providedat the back of said skin layer board fulfill the function of said pipes(i.e., a comparatively small number of pipes for collectively exhaustingthe temperature controlling gas passed through the vents). This spacescan be obtained by, for example, providing numerous convexes, each ofwhich is islandishly isolated over the surface of the heat insulatingboard, and supporting the back surface of said skin layer board at theapexes of said numerous convexes. This allows the spaces provide at theback of the skin layer board to fulfill the performance of said pipes.This skin layer may be provided all over the mold surface, but may alsobe provided only over a portion which should have high transferability.

The skin layer board having said vents should preferably be capable ofwithstanding the pressure from the polymer side and not easily bedegraded in the environment in which the skin layer board is repeatedlyexposed to the molten polymer. Therefore, as a material of the skinlayer board, nickel, nickel alloy, nickel chrome alloy, chrome alloy,aluminum alloy or austenitic stainless steel is preferable. The thermalconductivity of the heat insulating layer comprising said skin layerboard and the spaces provide at the back thereof should be within arange of 0.05 to 0.5 [cal/cm·s·° C.], preferably be within a range of0.07 to 0.4 [cal/cm·s·° C.], and more preferably be within a range of0.08 to 0.1 [cal/cm·s·° C.]. If this thermal conductivity is higher than0.5 [cal/cm·s·° C.], the time required for heating to a desiredtemperature level will be excessively long, which is not practical. Ifsaid heat conductivity is lower than 0.05, cooling will require longertime, and molding cycle will require longer time, which is notpractical, either. In order for the surface temperature of said skinlayer to be raised to a desired temperature level, the heat capacity ofthe skin layer should preferably be small. For this purpose, thethickness of said skin layer should be within a range of 10 to 2000 μm,preferably be within a range of 50 to 1000 μm, and more preferably bewithin a range of 80 to 500 μm.

The preheating of the mold surface can also be achieved by heating themold surface from the back side.

For example, such preheating can be achieved by adiabatically supportinga member composing the mold surface (hereinafter referred to as “moldsurface member”) in the state with spaces provided at the back of saidmold surface member and injecting and exhausting the temperaturecontrolling gas into and out of said spaces. As an example of suchmechanism for supporting said mold surface member in the state withspaces provided at the back of said mold surface member, a mechanismprovided with numerous convexes, each of which is islandishly isolatedover the surface of the heat insulating board, for supporting the backsurface of said mold surface member at the apexes of said numerousconvexes is conceivable. Furthermore, a mechanism which is provided withnumerous ribs over the back surface of the mold surface member and alsoover the surface of the heat insulating board, both ribs being arrangedin such a positional relationship that both ribs over the back surfaceof the mold surface member and the ribs over the surface of the heatinsulating board intersect each other, for supporting the back of themold surface member with the heat insulating board, can also beconceivable.

As examples of polymers to which the molding methods according to thepresent invention can be applied, thermoplastic resins, thermosettingresins, thermoplastic elastomers, natural rubbers and synthetic rubberscan be conceivable.

As examples of these polymers, thermoplastic resins with a plasticizingtemperature range of 50 to 450° C. can be used with no particular limit.Specifically, for example, a mixture of one or more polymers, such asstyrene resins (e.g., polystyrene, butadiene-styrene copolymer,acrylonitrile-styrene copolymer, acrylonitrile-butadiene-styrenecopolymer), ABS resins, AES resins, AAS resins, polyethylene,polypropylene, ethylene-propylene resins, ethylene-ethylacrylate resins,polyvinyl chloride, polyvinylidene chloride, polybutene, polycarbonate,polyacetal, polyphenylene oxide, polymethylmethacrylate, saturatedpolyester resins (e.g., hydroxycarboxylic acid condensates likepolylactic acid, condensates of diol and dicarboxylic acid, such aspolybutylene succinate), polyamide resins, fluorocarbon resins,polysulfone, polyether sulfone, polyarylate, polyether ether ketone, andliquid-crysal polymer can be named.

Among these thermoplastic resins, polystyrene, butadiene-styrenecopolymer, acrylonitrile-styrene copolymer, ABS resins, AES resins, AASresins, polyethylene, polypropylene, polyvinyl chloride, saturatedpolyester resins, and polyamide resins are preferable.

Thermosetting resins can be used with no particular limit. For example,epoxy resins, acrylic resins, urethane resins, epoxy-urethane resins,and acrylic urethane resins can be named.

As examples of thermoplastic elastomers, styrene thermoplasticelastomers (abbreviated as SBCs. Hereinafter abbreviated is indicated inparenthesis), olefine thermoplastic elastomers (TPOs), urethanethermoplastic elastomers (TPUs), ester thermoplastic elastomers (TPEEs),and amide thermoplastic elastomers (TPAEs) according to theclassification by hard segment chemical composition can be named. Inaddition to the above, polyvinyl chloride thermoplastic elastomers(TPVCs), homopolymer type syndiotactic 1,2-polybutadiene, ion clustertype thermoplastic elastomers (ionomers), and fluorinated thermoplasticelastomers containing fluorocarbon resins as arrester blocks can benamed. For the information purpose only, of all thermoplastic elastomerscomposed by means of resin-rubber blending, TPOs with dynamiccross-linking for performance improvement by kneading rubber component,which are used for soft segment, and breaking up dispersed rubberparticle size are particularly called “TPVs” in some cases. As suchthermoplastic elastomers, a mixture of one or more of these polymers canbe named.

As SBCs, styrene-butadiene-styrene block copolymers (SBSs),styrene-isoprene-styrene block copolymers (SISs), styrene-ethylenebutylene-styrene block copolymers (SEBSs), functional group applied typeSEBSs (f-SEBSs), styrene-ethylene propylene-styrene block copolymers(SEPSs), and random type hydrogen applied styrene butadiene polymers(HSBRs) are preferable.

As TPOs, simply blended type TPO in which polyolefins, such as PP andPE, is mixed with elastomer, such as EP, EPDM, EBM and EBDM, andcompounded in a blender, such as Banbury and Labo Plastomill (s-TPO),implanted TPO in which olefin monomer, which is used for hard segment,is copolymerized, and then olefin monomer, which is used for softsegment, is copolymerized in the same plant or in the same reactor (theprocess flow may be reversed) (i-TPO), and dynamically vulcanized TPO inwhich rubber is mixed and vulcanized simultaneously in a blender, suchas Banbury and Labo Plastomill (TPVs) are preferable. As TPVs, PP-EPDMwhich is a combination of PP used for hard segment and EPDM used forsoft segment (hereinafter, the left part of polymer name refers to hardsegment, and the right part of polymer name refers to soft segment),PP-nitrile rubber (NBR), PP-acrylic rubber (ACM), PP-natural rubber(NR), PP-butyl rubber (IIR), PE-EPDM, PE-NR, nylon-NBR, nylon-ACM,polyester-chloroprene (CR), and PVC-NBR are preferable.

As TPUs, TPU in which diisocyanate used for hard segment is toluenediisocyanate, TPU in which diisocyanate used for hard segment is4,4′-diphenylmethane diisocyanate, TPU in which diisocyanate used forhard segment is 1,6-hexamethylene diisocyanate, TPU in whichdiisocyanate used for hard segment is 2,2,4(2,4,4)-trimethylhexamethylene diisocyanate, TPU in which diisocyanate used for hardsegment is p-phenylene diisocyanate, TPU in which diisocyanate used forhard segment is 4,4′-dicyclohexylmethane diisocyanate, TPU in whichdiisocyanate used for hard segment is3,3′-dimethyldiphenyl-4,4′-diisocyanate, TPU in which diisocyanate usedfor hard segment is 1,5′-naphthalene diisocyanate, TPU in whichdiisocyanate used for hard segment is trans-1,4-cyclohexyl diisocyanate,TPU in which diisocyanate used for hard segment is lysine diisocyanate,and mixtures of two or more of these TPUs are preferable.

As TPEEs, polyester-polyether type TPEE in which aromatic crystallinepolyester is used for hard segment and polyether is used for softsegment, polyester-polyester type TPEE in which aromatic crystallinepolyester is used for hard segment and aliphatic polyester is used forsoft segment, and liquid crystalline TPEE in which liquid crystalmolecules are used for hard segment and aliphatic polyester is used forsoft segment are preferable. As polyester-polyether type TPEEs, eitherof polycondensate in which butanediol and dimethyl terephthalate,polycondensate in which ethylene glycol and dimethyl terephthalate,polycondensate in which butanediol and 2,6-naphthalene dicarboxylicacid, polycondensate in which ethylene glycol and 2,6-naphthalenedicarboxylic acid, or mixture of these polycondensates are used for hardsegment, and polycondensate in which either ofpolytetramethyleneetherglycol, poly(1,2-poropylene oxid)glycol,poly(ethylene oxid)glycol, or mixture of these glycols is used for softsegment is more preferable. As polyester-polyester type TPEEs, TPEE inwhich hard segment is the same as polyester-polyether type TPEE butpolylactone type aliphatic polyester is used for soft segment is morepreferable. As liquid-crystal TPEEs, multi-block copolymer in whichthermotropic liquid-crystal polymer, particularly low-molecularliquid-crystal compound, such as dihydroxy-paraquarter-phenyl, is usedfor hard segment, and aliphatic polyester is used for soft segment ismore preferable.

As TPAE, multi-block copolymer in which polyamide is used for hardsegment and low-Tg polyether or polyester is used for soft segment ispreferable, and copolymer in which nylon-6, nylon-6,6, nylon-6,10,nylon-11 or nylon-12 is used for hard segment and polyetherdiole orpolyesterdiol is used for soft segment is more preferable, and copolymerin which at least one of diolpoly(oxytetramethylene)glycol,poly(oxypropylene)glycol, poly(ethyleneadipate)glycol andpoly(butylene-1,4-adipate)glycol is used for soft segment isparticularly preferable.

As TPVCs, TPVC in which high-molecular weight polyvinyl chloride (PVC)is used for hard segment to give the function of cross-linking point atmicrocrystalline part, and PVC plasticized with plasticizer is used forsoft segment, TPVC in which PVC introduced with partially cross-linkedconstruction or branch construction is used for soft segment and PVCplasticized with plasticizer is used for soft segment, and TPVC in whichPVC is used for hard segment and partially cross-linked NBR or similarrubber and/or TPE, such as TPU and TPEE, is used for soft segment, ormixture of two or more of these TPVC are preferable.

Natural rubbers can be used with no particular limit. For example, oneof gum Arabic, karaya rubber or the like or mixture of two or more ofthese natural rubbers can be named.

Synthetic rubbers can be used with no particular limit. For example,polybutadiene rubber, polyisoprene rubber, isobutylene-isoprene rubber,ethylene-α-olefin-(diene) copolymer (e.g., EPM, EBM, EOM, EPDM, EBDM),aromatic-vinyl-compound-conjugate-compound-(α-olefin) copolymer (e.g.,SBR, SBS, SEBS), acrylonitrile-butadiene rubber, fluorocarbon rubber,silicone rubber, butyl rubber halide (e.g., butyl rubber chloride, butylrubber bromide), and mixture of two or more of these synthetic rubberscan be named.

The above-described thermoplastic resins, thermosetting resins,thermoplastic elastomers, natural rubbers and synthetic rubbers can beused in a form of alone or multi-mixture.

As far as it does not impair the objects of the present invention, theabove-described polymers can be blended with a cross-linking agent, avulcanization acceleration aid, a vulcanization activator, a filler, ananti-oxidant, a processing aid, a softener, a lubricant, a lightstabilizer, an antibacterial agent, and other additives.

The foaming agent used in the molding methods according to the presentinvention varies according to the type of the polymer to be used as amolding material. For example, a well-known inorganic or organic foamingagent can be used. As specific examples of the foaming agent, sodiumbicarbonate, ammonium bicarbonate, sodium carbonate, ammonium carbonate,azodicarboxylic amide, dinitrosopentamethylene tetramine,dinitrosotelephthalic amide, azobisisobutyronitrile, azodicarboxylicbarium, and sulfonyl hydrazides such as toluenesulfonyl hydrazide can benamed.

Among of all, azodicarboxylic amide, dinitrosopentamethylene tetramine,and sulfonyl hydrazides are more preferable.

These foaming agents may be used in combination with a well-knownfoaming aid for urea, urea derivatives or the like.

The blending ratio of the foaming agent varies depending on the type ofthe polymer as a molding material and the use of the molded product. Forexample, 100 parts by weight of polymer, 0.5 to 30 parts by weight ofthe foaming agent is preferable, and 1 to 15 parts by weight of thefoaming agent is more preferable. If the foaming agent is used toolittle, foam with only a low expansion ratio could be obtained, and if30 or more parts by weight of the foaming agent is used, gas generatedby the decomposition of the foaming agent might be excessive, abnormallyraising gas pressure and resulting in foam with cracks.

As examples of the uses of molded products molded by the molding methodsaccording to the present invention, stationery products (e.g., deskmats, cutting mats), car interiors or exteriors (e.g., interior panels,assist grips, instrumental panel skin materials, bumper materials),civil engineering materials (e.g., facing films, waterproof mats), shoesmaterials (e.g., shoe soles), sports goods (e.g., head gear, shoulderpads), semiconductor-related parts, medical materials, food-relatedmaterials, office automation equipment-related parts, audio visual andhousehold electrical appliance parts and office equipment parts can benamed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view illustrating the cross section of molds usedfor the injection molding method of the first preferred embodimentaccording to the present invention, where FIG. 1( a) illustrates a casewhere a gas injection pipe 51 is provided in the same position as amolten resin injection nozzle 41, and FIG. 1( b) illustrates a casewhere the gas injection pipe is used also as a gas exhaust pipe;

FIG. 2 is a schematic view illustrating the cross section of a mold usedfor the injection molding method of the first preferred embodimentaccording to the present invention, and illustrating a case where a gasinjection pipe is used also as a gas exhaust pipe and provided in thesame position as a molten resin injection nozzle 41;

FIG. 3 is a descriptive view illustrating an injection molding processperformed with the mold of FIG. 1( a), where FIG. 3( a) illustrates aprocess in which gas is injected at the same time when molten resin isinjected, and FIG. 3( b) illustrates a process in which gas is exhaustedand thereby the inside of molten resin is foamed;

FIG. 4 is a schematic view of the cross section of a mold used for theinjection molding method of the second preferred embodiment according tothe present invention, where a difference from FIG. 1 lies in thatmolten resin is released into a shelter 57;

FIG. 5 is a descriptive view of the operation of a mold used for aconventional injection molding method, and illustrating a process inwhich molten resin is injected and then a lower mold 120 is displacedand thereby the cavity space is enlarged;

FIG. 6 is a schematic view of the cross sections of a mold used for theinjection molding method of the third preferred embodiment according tothe present invention, where FIG. 6( a) illustrates a case where a gasinjection pipe 51 is provided in the same position as a molten resininjection nozzle 41, and FIG. 6( b) illustrates a case where the gasinjection pipe is also used as a gas exhaust pipe, where both cases haveheat insulating layers 15 and 25;

FIG. 7 is a schematic view of a mold used for the injection moldingmethod of the fourth preferred embodiment according to the presentinvention, illustrating a case where a gas injection pipe is used alsoas a gas exhaust pipe and provided in the same position as a moltenresin injection nozzle 41, where said case has temperature control gasinjection pipes 18 and 28, temperature control gas exhaust pipes 19 and29 and mold surface members 17 and 27; and

FIG. 8 is a detailed view illustrating the cross section of the moldsurface member 17 (27) of FIG. 7.

PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments according to the present inventionwill be described referring to the drawings.

(1) First Preferred Embodiment

FIG. 1( a), (b), and FIG. 2 are schematic views illustrating the crosssection of molds used for the injection molding method of the firstpreferred embodiment according to the present invention. FIG. 1( a)illustrates a structure in which a gas injection pipe 51 is provided inthe same position as a molten resin injection nozzle 41. FIG. 1( b)illustrates a structure in which a pipe 54 is used both as a gasinjection pipe and as a gas exhaust pipe. FIG. 2 illustrates a structurein which a pipe 53 is used both as a gas injection pipe and as a gasexhaust pipe and provided in the same position as a molten resininjection nozzle 41.

According to the structure illustrated in FIG. 1( a), molten polymer isinjected through an injection molding nozzle 41 of an injection machine40 into a cavity (in-mold space) 30 formed by an upper mold 10 and alower mold 20, and at the same time, high-pressure gas (air) is injectedthrough a gas injection pipe 51 provided in the same position as theinjection molding nozzle 41 into the molten polymer.

The distribution of molten polymer 60 at this time is illustrated inFIG. 3( a). As illustrated in this figure, the molten polymer 60 is inadhesion to the whole area of the mold surface.

The pressure of gas in injection is properly set according to the typeof molten polymer, injection pressure, mold surface temperature, volumeand shape of the cavity 30 and others.

The gas is exhausted through a gas exhaust pipe 52 with timing in whichthe skin layer of the molten polymer injected in the manner as describedabove is cooled and solidified. The gas may be exhausted by making thegas exhaust pipe 52 communicated with the outside (i.e., by not placingthe exhaust pressure of the gas under positive control but by having thegas is pushed out by the foaming pressure of the molten polymer), oralternatively it may be so arranged that a valve mechanism or the likeis incorporated in the gas exhaust pipe 52 so that the pressure within acavity 30 (i.e., the internal pressure of the molten polymer) canundergo a transition according to a desired pressure pattern, andthereby the exhaust gas pressure can be regulated. Here, the desiredpressure pattern refers to a pressure pattern set so that the inside ofa molded product can be foamed with a desired expansion ratio, and theabscissa axis is taken as time axis.

The volume occupied by the molten polymer increases and the pressuredecreases as the gas exhaust develops, and therefore the molten polymerfoams. A condition in which a molded product comprising a skin layer 61and an internal foamed layer 62 has been molded is illustrated in FIG.3( b).

The above description uses the structure illustrated in FIG. 1( a). Whenthe structure illustrated in FIG. 1( b) is used, injection molding ismade in the same way as the above but with a difference that a pipe 54is used both for gas injection and for gas exhaust. Also, when thestructure illustrated in FIG. 2 is used, injection molding is made inthe same way as the above but with a difference that a pipe 53 is usedboth for gas injection and for gas exhaust and the pipe 53 is provide inthe same position as a molten resin injection nozzle 41.

(2) Second Preferred Embodiment

FIG. 2 is a schematic view illustrating the cross section of a mold usedfor the injection molding method of the second preferred embodimentaccording to the present invention. According to the second preferredembodiment, a part of molten polymer injected into a cavity 30 isreleased into a shelter 57, and thereby the volume occupied by themolten polymer is increased, the pressure is decreased, and the insidethereof is foamed.

Timing with which a part of the molten polymer is released into theshelter 57 is timing with which the skin layer (portion contacted closeto the mold cavity surface) of the molten polymer injected into thecavity 30 is cooled and solidified. When this timing comes, a shutter 56is opened, and a part of the molten polymer within the cavity 30 isreleased into the shelter 57.

Here, the shutter may be omitted by properly setting the volume of thecavity 30, the volume of the shelter 57, the diameter of a passagecommunicating between the cavity 30 and the shelter 57 and others. Thatis, when the skin layer of the injected molten polymer is quicklyformed, a part of the molten polymer can be released into the shelterfrom the very start of the injection of the molten polymer. In thiscase, as there is no need to control the open/close operation of theshutter, the molding process control can be simplified this much.

(3) Third Preferred Embodiment

FIG. 6( a) and FIG. 6( b) are schematic views of the cross section ofmolds used for the injection molding method of the third preferredembodiment according to the present invention. Each of the molds of FIG.6( a) and FIG. 6( b) is roughly the same as each of the molds of FIG.(a) and FIG. 1( b) according to the first preferred embodiment. Adifference there between lies in that each of the molds of FIGS. 1( a)and 1(b) has no heat insulating layer while each of the molds of FIG. 6(a) and FIG. 6( b) has heat insulating layers (a heat insulating layer 15of an upper mold 10, and a heat insulating layer 25 of a lower mold 20).Due to the provision of these heat insulating layers, each of the moldsof FIG. 6( a) and FIG. 6( b) has higher transferability than each of themolds of FIG. 1( a) and FIG. 1( b) has, provided that all otherconditions are the same.

(4) Fourth Preferred Embodiment

FIG. 7 is a schematic view of a mold used for the injection moldingmethod of the fourth preferred embodiment according to the presentinvention, and FIG. 8 is a detailed view of the cross section of a moldsurface member 17 (27) of FIG. 7. The mold surface member 17 (27) isprovided with gas both exhausting function and heat insulating function.

The mold illustrated in FIG. 7 is roughly the same as the mold of FIG. 2according to the first preferred embodiment. Differences therebetweenlie in that the mold of FIG. 2 has no temperature controlling gasinjection mechanism while the mold of FIG. 7 has a temperaturecontrolling gas injection mechanism (injection pipes 18 and 28) and thatthe mold surface of the mold of FIG. 2 is formed as a surface of themold body while the mold surface of the mold of FIG. 7 is formed withthe mold surface members 17 and 27 having temperature controlling gaspassing and exhausting functions and temperature holding function bymeans of heat insulation.

When the mold of FIG. 7 is used, heated gas is injected into a cavity 30through gas injection pipes 18 and 28 before the molten polymer isinjected into a cavity 30. Thereby, the molding surfaces of the moldsurface members 17 and 27 (i.e., surfaces exposed to the cavity 30) areheated to a desired temperature level. On the other hand, the heated gasinjected into the cavity 30 is exhausted to the outside through spaces63 (FIG. 8) and through gas exhaust pipes 19 and 29. For thisarrangement, the mold of FIG. 7 has higher transferability that the moldof FIG. 2 has, provided that all other conditions are the same.

Finally, the mold surface member 27 of the lower mold 20 will bedescribed referring to FIG. 8. Here, it should be noted that the moldsurface member 17 of the upper mold 10 is also structured in the sameway. The mold surface member 27 of the lower mold 20 comprises a skinlayer board 60 of 500 μm thick made of nickel and a numerous projections65 islandishly isolated from each other all over the back surface ofsaid skin layer board 60. These projections 65 are to provide spaces 63between the skin layer board 60 and the surface of the lower mold 20.According to this preferred embodiment, spaces of 200 μm high or so eachare provided. Alternatively, these projections 65 maybe provided overthe surface of the lower mold 20, or over both the back surface of theskin layer board 60 and the surface of the lower mold 20 (unless bothprojections are not coincided with each other). The skin layer board 60with a surface 61 serving as a mold surface is provided with numerousvents 62. The diameters of these vents 62 are 100 μm or so each on theside of the cavity 30 and 800 μm or so each on the side of the spaces63. These vents 62 are communicated with a gas exhaust pipe 29 providedwithin the lower mold 20 through the spaces 63, and the other end ofsaid gas exhaust pipe 29 is communicated to the outside.

EXAMPLES

Working examples molded by using the molding methods according to thepresent invention will be described.

Thermoplastic elastomer: Sixty-eight parts by weight ofethylene-propylene-5-ethylidenenorbornen copolymerized rubber(manufacturer: JSR Corporation; product name: “EP98A;” ethylenecontents: 79 mol %; propylene contents: 21 mol %; iodization: 15;paraffinic oil: 75 phr oil extension), 10 parts by weight of linearlow-density polyethylene (LLDPE) (manufacturer: Japan Polychem Corp.;product name: “UF423”), 17 parts by weight of hydrogenated dienecopolymer (Manufacturer: JSR Corporation; a trade name: “DYNARONDR6200P”), 5 parts by weight of propylene-ethylene block polymer(manufacturer: Japan Polychem Co., Ltd.; product name: “BC5CW”) ascrystalline-α-olefin copolymer, and 0.2 parts by weight of anti-oxidant(manufacturer: Chiba Specialty Co., Ltd.; product name: “Irganox 1010”)were weighed, hot-kneaded in a 10-liter pressure kneader (manufacturer:Moriyama Seisakusho Co., Ltd.) at a preset temperature of 150° C. for 15minutes at a rotational speed of 32 rpm (the former half of thekneading) and 28 rpm (the latter half of the kneading). The obtainedcomposition in the molten state was pelletized, and thus the aimedthermoplastic elastomer was obtained.

Foaming agent: Manufacturer: Eiwa Chemical Ind. Co., Ltd., Product name:Foaming Agent Master Batch Elastoren EE206.

By using 95 parts by weight of this thermoplastic elastomer and 5 partsby weight of Elastoren EE206, the following products were molded:

Example 1 According to the First Preferred Embodiment

The above-described pellet-blended thermoplastic elastomer and foamingagent were pellet-blended and mold-injected and gas was injected at thesame time, and then the gas was slowly exhausted. As a result, a moldedproduct with adequate appearance and feel and the foamed inside wasobtained.

Example 2 According to the Second Preferred Embodiment

The above-described pellet-blended thermoplastic elastomer and foamingagent were pellet-blended and mold-injected, and after the mold cavitywas filled with the molten polymer, the shutter was opened to increasethe volume of the molten polymer. As a result, a molded product withadequate appearance and feel and the foamed inside was obtained.

1. A method for molding a polymer comprising the steps of, putting apolymer containing a foaming agent into a mold cavity while contactingthe polymer in a molten state close to the surface of the mold cavity,communicating the mold cavity with a shelter to release a part of thepolymer to the shelter by foaming pressure and increase a volume to beoccupied by the polymer while maintaining the inside shape of the moldcavity, and obtaining a molded product having an outside shape thereoffit to the inside shape of the mold cavity and the inside thereof madefoamed, wherein the mold cavity is communicated with the shelter byopening a shutter provided in a passage between the mold cavity and theshelter.
 2. A method for molding a polymer according to claim 1, whereinthe entirety or a part of the surface of the mold cavity is heatinsulated by providing spaces at the back of the surface and/orcomposing the surface with a porous metal.
 3. A method for molding apolymer according to claim 1, wherein the mold cavity is communicatedwith the shelter by a passage having a predetermined diameter.
 4. Amethod for molding a polymer comprising the steps of, putting a polymercontaining a foaming agent into a mold cavity being communicated with ashelter, contacting the polymer in a molten state close to the surfaceof the mold cavity to cool and solidify a surface portion, and form askin layer while releasing a part of the polymer to the communicatedshelter to increase a volume to be occupied by the polymer whilemaintaining the inside shape of the mold cavity, and obtaining a moldedproduct having an outside shape thereof fit to the inside shape of themold cavity and the inside thereof made foamed, wherein the mold cavityis communicated with the shelter by opening a shutter provided in apassage between the mold cavity and the shelter.
 5. A method for moldinga polymer according to claim 4, wherein the entirety or a part of thesurface of the mold cavity is heat insulated by providing spaces at theback of the surface and/or composing the surface with a porous metal. 6.A method for molding a polymer according to claim 4, wherein the moldcavity is communicated with the shelter by a passage having apredetermined diameter.